This invention relates to a power distribution line protection system, and more particularly to a protection and coordination method of a fault detection relay provided at the power outlet from a substation to a distribution line and fault detection relays arranged on the distribution line in the protection system.
In order to quickly discriminate an affected section from sound sections of a distribution line upon occurrence of a fault on the distribution line, conventionally "section switches for automatic detection of the affected section" has been used (e.g., "Denki Kogaku Handbook (Electric Engineering Handbook)" published by the Institute of Electrical Engineers of Japan, February, 1988, page 1264). According to this handbook, after all section switches are opened upon occurrence of the fault, they are automatically closed one after another at preset time intervals. At the moment the fault detection relay installed at the power outlet from a substation to the distribution line involved in the fault detects the fault, a relevant breaker at the power outlet of the distribution line opens. From the section switch which was closed just before the above-mentioned operation, the section that the fault exists can be identified. This is generally called the time delayed sequential circuit closing system. The time delayed sequential circuit closing system is also disclosed in "Haiden Gijutsu Sougou Manual (General Manual for Power Distribution Technology), first edition, Ohm-sha, pp. 462-467.
According to the conventional time delayed sequential circuit closing system, there is a possibility that some sound section can be involved in the power service interruption caused by the fault, and time of (the number of switches having the time delayed sequential circuit closing function).times.(circuit closing interval (e.g., in minutes)) is required for completing the power transmission up to the end of the distribution line. A resulting problem is that the power failure time is longer for the areas closer to the end of the distribution line. If the number of switches with the time delayed sequential circuit closing function is reduced to shorten the power interruption time, a protected section (power-interrupted section) will become longer. The time delayed sequential circuit closing system has a problem that the sound sections may suffer power interruption time twice, that is, a power interruption when a fault occurs and a power interruption when the affected section is detected.